A third-year medical student is examining a patient who has acute onset of abdominal pain. The patient is a 65-year-old smoker with HTN and DM who has had dull abdominal pain gradually building for the last 12 hours. It is not related to food nor relieved by taking famotidine. On physical examination, auscultation reveals a bruit. Palpation shows a pulsatile mass. While lightly palpating the epigastrium, the patient suddenly becomes hypotensive and passes out.
What is the most likely diagnosis?